Abstract
ObjectivesThe marine benthic nitrogen cycle is affected by both the presence and activity of macrofauna and the diversity of N-cycling microbes. However, integrated research simultaneously investigating macrofauna, microbes and N-cycling is lacking. We investigated spatio-temporal patterns in microbial community composition and diversity, macrofaunal abundance and their sediment reworking activity, and N-cycling in seven subtidal stations in the Southern North Sea.Spatio-Temporal Patterns of the Microbial CommunitiesOur results indicated that bacteria (total and β-AOB) showed more spatio-temporal variation than archaea (total and AOA) as sedimentation of organic matter and the subsequent changes in the environment had a stronger impact on their community composition and diversity indices in our study area. However, spatio-temporal patterns of total bacterial and β-AOB communities were different and related to the availability of ammonium for the autotrophic β-AOB. Highest bacterial richness and diversity were observed in June at the timing of the phytoplankton bloom deposition, while richness of β-AOB as well as AOA peaked in September. Total archaeal community showed no temporal variation in diversity indices.Macrofauna, Microbes and the Benthic N-CycleDistance based linear models revealed that, independent from the effect of grain size and the quality and quantity of sediment organic matter, nitrification and N-mineralization were affected by respectively the diversity of metabolically active β-AOB and AOA, and the total bacteria, near the sediment-water interface. Separate models demonstrated a significant and independent effect of macrofaunal activities on community composition and richness of total bacteria, and diversity indices of metabolically active AOA. Diversity of β-AOB was significantly affected by macrofaunal abundance. Our results support the link between microbial biodiversity and ecosystem functioning in marine sediments, and provided broad correlative support for the hypothesis that this relationship is modulated by macrofaunal activity. We hypothesized that the latter effect can be explained by their bioturbating and bio-irrigating activities, increasing the spatial complexity of the biogeochemical environment.
Highlights
Coastal marine sediments play a pivotal role in the ecology of shallow marine ecosystems
Our results indicated that bacteria showed more spatio-temporal variation than archaea as sedimentation of organic matter and the subsequent changes in the environment had a stronger impact on their community composition and diversity indices in our study area
Community composition of total bacteria, total archaea and the β-ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) were all significantly affected by an interaction between months and stations
Summary
Coastal marine sediments play a pivotal role in the ecology of shallow marine ecosystems They receive up to 30% of the pelagically produced organic matter [1], which is mineralised and returned to the water column as inorganic nutrients [2], further supporting primary and secondary production. The activities of the macrofauna result in additional complexity within the sediment matrix This affects microbial abundance [21,22], diversity [23] and activity—mineralization, nitrification and denitrification [24,25,26,27,28]. Integrated studies including different sediment types, repeated over time, investigating the link between natural macrofaunal community, microbial communities and rates of ecosystem functioning are not available yet
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